1. Field of Invention
The present invention relates to a spiral concentrically wound Bourdon tube. Specifically, the present invention relates to a spiral concentrically wound Bourdon tube having the post area parallel to the coil area and the complete design is all on the same plane.
2. Background of the Invention
The industry standard version of a spiral concentrically wound Bourdon tube would have a 90-degree bend on the rounded stem area that would be called the perpendicular post area of the coil. While conventional spiral concentrically wound Bourdon tubes are easily mounted on the closed end of a core, pipe, or other pressure vessel to create a pressure gauge, such that the post or stem is perpendicular to the Bourdon tube coil plane, the assembly has disadvantages when the gauge must function in extreme conditions such as those found in automotive environments, for example on a tire valve stem. Such disadvantages include limitations as to the orientation of the gauge dial or Bourdon tube coil plane relative to the pressure vessel and fluid flow path, the propensity for such Bourdon tubes and their gauge assemblies to leak or become damaged when exposed to rotational forces and other forces or environmental conditions, and the difficulty in creating gauges with flow-through functionality without exacerbating these disadvantages or increasing the cost of such gauges.
Bourdon tubes are a frequently used technology for measuring fluid pressure, relative to ambient or atmospheric pressure. In practice, a Bourdon tube pressure gauge is comprised of a flattened thin-wall, closed-end tube with the open hollow end connected to a fixed pipe or vessel containing the fluid pressure to be measured. The closed end of the Bourdon tube may be connected to a lever (indirect drive) or not (direct drive). Pressure changes in the pipe or vessel are transmitted to the Bourdon tube, which then changes its shape in a predictable way, allowing for pressure to be measured by the movement of the Bourdon tube in response to pressure changes in the Bourdon tube. Bourdon tubes are currently available in 3 basic designs: C-tube, concentric with perpendicular post, and helical. A C-tube is named after its shape where the tube is wound or curved through less than 360 degrees of arc. A concentrically wound Bourdon tube with a perpendicular post is one where the flattened tube is wound concentrically around the unsealed end which is bent and oriented such that the post is perpendicular to the plane of the concentric Bourdon tube coil windings. A helical tube is named after the helical shape that the tube is wound in.
C-tubes are generally used for high-pressure applications greater than 500 pounds per square inch (PSI). They also are generally too large to be used for gauges that are mounted on tires, or other applications where a small, light gauge is needed. Helical Bourdon tubes also cannot be used in a gauge small enough to use in valve stem-mounted tire gauges. Concentric perpendicular post Bourdon tubes are generally smaller and lighter than C-tubes, and more suited to low-pressure (<500 PSI) applications, but are difficult to use in flow-through gauges without adding significant expense and weight in the form of extra parts to provide for flow-through gauge functionality, and are not rugged enough to withstand the extreme conditions endemic to certain automotive environments. Additionally, in order to make a gauge that will face out from a wheel to facilitate reading the gauge, a different concentric perpendicular post Bourdon tube must be made for each side of the vehicle in order to prevent wheel rotation from unwinding the tube, one that is wound clockwise, and one that is wound counter-clockwise, adding additional costs to the manufacturing of such gauges.